Aquariums often include filters to remove waste matter including detritus, excess food, free-floating particulate and chemicals from the water. Commonly, filters are mounted over the side of an aquarium; however, other arrangements may be provided where filters are submersed in the tank or free standing. Filters displace water laden with waste matter from the tank and direct it to a filter element. Most of the waste matter is removed from the water as the water passes through the filter element. The water then circulates back into the tank. Optionally, the water may be aerated prior to re-entering the tank.
Often a filter element is designed to mechanically remove the waste matter from the aquarium. When a filter element becomes clogged, water cannot pass through the filter and bypasses around the filter element. The filter element must then be cleaned or replaced to ensure that water is being filtered as it passes through the aquarium filter. However, filter elements are generally concealed within a filter housing. Although the housing improves the aesthetics of the filter, it does not allow the casual observer to notice when the filter element has become clogged with waste matter.
Mechanical indicators have been used to indicate rising water levels or the flow of water through the filtration system. However, such mechanical indicators may get stuck or fouled with debris. Other indicators, such as timers, do not necessarily reflect the actual efficiency of the filter, but just predict efficiency. Accordingly, room remains for improvement in indicating filtration efficiency.